Method for recovering pyridine and tar bases from hot coke oven gases



July 16, 1957 M. P. swEENEY 2,799,678

METHOD FOR REcovERING PYRIDINE AND TARd BASES FROM HOT COKE OVEN GASES 2 Sheets-Sheet 1 Filed Nov. 15, 1955A "2 Sheets-Sheet 2 July 15, l957 M. P. swEENEY METHOD FOR REOVERINGV PYRIDINE AND TAR-BASES FROM HOT com: OVEN GASES Filed Nov. 15, 1955 v United States Patent METHOD FR RECOVERNG PYRIDINE ANDTAR BASES FROM EGT CKEOV'EN GASES Maxwell Patrick Sweeney, 'Glenoldem Pa., yassignonto United Engineers & Constructors Inc., a corporation of Delaware Application November 15, 1955, Serial No. 546,873

6 Claims. (Cl. 2,60-290) The present invention relates :to a coke ioven byproduct .recovery process, and more particularly to -a v-rnethod `for recovering pyridine and tar .bases .from hot coke =oven gases.

In .the destructive distillation of natural carbonaceous materials such as coal, lig-nite, peat and the like, Ahot gases are .produced ,containing various compound-s whose recovery is economically desirable. Among these lare Ithe so-called pyridine and tar bases. The term pyridine and tar bases is used to indicate compounds normally recovered `from .coke oven gases which -have a basic reac tion. Among these compounds the principal ones are pyridines, picolines, lutidines, collidines, and quinolines.

Specific pyridine and tar base compounds which have been isolated from coke oven gases include pyrrole, pyridine, Vaniline, Z-methyl pyridine, -ortho-toluidine, 2,3-di methyl pyridine, indole, l,2,3,4-tetramethyl pyridine, quinoline, isoquinoline, 2-methyl quino'line, 'l-methyl isoquinoline, l-naphthylamine, 2,'8-dimethyl quinoline, carbazole, acridine, phenanthradine, hydroacridne, Z-methyl carbazole and benzocarbazole.

The total amount of pyridine and tar bases recovered and the relative proportions of individual compounds, will depend on the nature of the carbonaceous material and Vthe conditions .of carbonization.

For many years, ynot much thought was given to the recovery of pyridine and tar bases as such. Recently, however, these compounds have grown in importance to chemical industry Vbecause of their increased use, for example, in the manufacture of waterproofing materials, sulpha drugs, and other medicinal products, organic chemicals, acrylic fibers and insecticides, with the result that therecovery of pyridine and tar bases has become an increasingly important part of coke oven by-product recovery practice.

In the class of byfproduct recovery processes to which the present invention is particularly applicable, the hot gases from the coke ovens are cooled and treated to remove tar therefrom. A certain amount of the basic compounds referred to above are removed along with the tar. The gases are subsequently further treated to remove ammonia and in this subsequent treatment more of the basic compounds referred to are removed. In accordance with the standard terminology of the art, that portion of the basic compounds removed with the tar will be referred to as tar bases and that portion remaining in the gases after tar removal and generally separated along with ammonia, will be referred to as pyridine bases. It will be understood that in general the same compounds appear in both the tar bases and the pyridine bases, although the proportions of individual compounds may be different in each group.

ln the most common type of by-product recovery processes n oW in use, at some point after the removal of tar from the coke oven gases, the gases are scrubbed with a strong mineral acid, such for example as sulphuric acid, usually in a device known as a saturator. The ammonia is removedvas the corresponding salt, for example, as

ammonium zsulphate, andthe pyridine `bases yare also removed from the vgases as salts, for example, as pyridine' sulphate. Various means are then used to spring and extract the `pyridine vbase-salts from Ethe `saturator liquor.

Methods for recovering NH3 lother than `those lemploying a saturator have been suggested, .as for example by Cole and Tannehill in U. S. Patent 2,162,838, "wherein a cooled aqueous liquor having substantially :no vapor pressure with respect to NH3 is used to scrub the last Atraces of ammonia from the gases.

In such processes, the pyridine -bases areremovedfrom the gases in a liquor containing NH3 'and acid gases rsuch as H28, HCN and CO2. The presence of `such acid fgases makes recovery of the pyridine -bases particularly diicult.

Tar bases, on the other hand, =in conventional processes, are extracted from the tar by the use of a mineral acid to ,give an aqueous liquor containing tar :base suphates, and are then separately sprung, :usually with caustic, and `extracted from the laqueous acid liquor.

Thus, the tar bases and the pyridine bases, despite ,their essentially .identical chemical nature, are 'conventionally recovered in two entirely different streams, involving a considerable expense in equipment Vand labor.`

It is an object of the present invention to provide a more eicient process for yrecovering tar bases 'and pyridine bases from coke oven gases, applicable to situations iin which the pyridine Ibases are removed lfrom vthe coke Ioven gases along with-acid gases and ammonia.

It is another object of the invention to provide la coke oven `by-product recovery process wherein tar bases can be recovered along with pyridine bases, `applicable to situations in which the pyridine bases are removed from the 'coke oven gases along with acid gases and ammonia.

Other -objects of the invention will be 'obvious from a consideration of the specification and claims.

According to the invention, in a coke oven byproduct recovery process in which tar and tar bases are removed from hot coke oven gases, and subsequently ammoniaand pyridine bases .are removed from the coke oven 'gases along with acid gases such .as HzS, HCN and CO2, the tar bases andthe pyridine bases are recovered by isolating the pyridine bases in a stream rich inammonia and free from acid gases, isolating the tar bases in an aqueous acid-tar bases liquor, and springing the tar bases from this liquor by means of the ammonia-pyridine bases stream. By this means, the tar bases and the pyridine bases are combined in a single stream and may be recovered with savings in equipment and labor.

The ammonia-pyridine base stream may be gaseous or it may be a liquid stream. If it is a gas, it can be made to serve a dual function of spring-ing the tar bases from the tar base salts and stripping the sprung tar bases from the liquid medium. l

The ammonia-pyridine base stream referred to should not contain substantial quantities of other reactive components, such for example, as CO2, HCN, or HzS. It may contain relatively large amounts of inert material such as H2O and N2. Generally, the ammonia-pyridine base stream will contain between about 5% and about inclusive by weight NH3 and between about 1% and about 10% inclusive by weight pyridine bases, usually between about 10% and about 30% inclusive ammonia, and between about 3% and about 6% inclusive by Weight pyridine bases. It Will Vbe understood, however, that these percentages are not critical to the invention and will vary with the recovery process employed.

The aqueous acid-tar base liquor referred to may con tain between about 1% and about 30% by weight mineral acid, usually H2804, between about '2% and about 40% by weight tar base salts, usually sulphates, and not more than about 50%r ammonium salts, usually ammonium sulphate. Preferably the liquor will contain between about 2% and about 10% by weight mineral acid, between about and about 30% by weight tar base salt, and between about and about 45% ammonium salt. Other constituents such as tar acids and neutral oils may be present in minor proportions.

Where the ammonia-pyridine base is a gas, the condi tions under which the stripping takes place will vary with the particular over-all recovery process employed. However, in general, the stripping column will be operated at a pressure of between about atmospheric and about l0 p. s. i. g., inclusive, preferably between about l and about 2 p. s. i. g. The temperature of the ammonia-pyridine bases stream will be generally between about C. and about 100 C., inclusive, preferably between about C. and about 95 C. The temperature of the acid-tar base liquor charged to stripping apparatus will usually be between about 20 C. and about 100 C., inclusive, preferably between about 60 C. and about C.

For the sake of illustration, the process according to the invention will be described in connection with modified Cole-Tannehill coke oven by-product recovery processes.

While it is considered that the invention is most advantageously used with the Cole-Tannehill process or modifications thereof, it will be understood that the invention is not limited to use with such processes, but may be employed with any coke oven by-product recovery process wherein the pyridine bases are removed from the coke oven gases along with ammonia and acid gases and may be concentrated in a stream rich in ammonia and having substantially no other reactive components and wherein tar bases are removed from the coke oven gases with the tar.

In the drawings:

Fig. 1 is a ow diagram of the preferred embodiment of the invention wherein the ammonia-pyridine base stream is a gaseous stream.

Fig. 2 is a iiow diagram of another embodiment of the invention wherein the ammonia-pyridine base stream is a liquid stream.

Referring now to Fig. 1 of the drawings, hot coke oven gases drawn from coke oven l pass overhead into a collecting main 2 where they are contacted with an aqueous ammoniacal flushing liquor injected into the main as at 3. This flushing liquor cools the gases, precipitates tar, and absorbs a certain amount of ammonia. The foul flushing liquors are removed from the gases through downcomer 4 whence they are delivered to ushing liquor decanter 5.

In the decanter 5, the flushing liquor forms into two layers, an upper aqueous layer which is recycled and used again in the collecting main, and a tar layer which is drawn off and processed to recover valuable components of the tar, as will be described below.

The coke oven gases passing through the downcomer 4 next move to a primary cooler scrubber 6, where they are contacted with an ammoniaeal liquor. in the primary scrubber 6, the gases are further cooled and from about 75% to about 95%, usually about 90% of the acid gases such as H28 and HCN are absorbed, together with between about 50% and about 90%, usually about 60% of the ammonia present in the gases.

The circulating liquor used in primary scrubber 6 is discharged to a circulating liquor decanter 7, where it, too, forms into a tar layer and an aqueous layer. Part of the aqueous layer is recycled for use in the scrubber 6 and part is delivered to a vacuum stripper rectilier 8 for further processing in a manner described below. The tar layer in circulating liquor decanter 7 is withdrawn and added to the tar drawn from flushing liquor decanter 5 for further processing.

The gases passing out of primary cooler scrubber 6 move to a naphthalene scrubber 9 where they may be contacted with an absorber oil for the removal of naphthalene. Details of a suitable naphthalene removal step may be obtained from the United States patent to G. L. Eaton, Number 2,649,403.

From the naphthalene scrubber 9, the gases are de livered to a pressure booster 10 where their pressure may be increased to an amount depending on the demand requirements and the pressure drop of downstream apparatus. Preferably, however, the pressure of the gases will be raised in booster 10 to above about 12 p. s. i. g.

The gases are then charged to an ammonia scrubber il where they are contacted with a lean mouoammonium phosphate solution for the removal of residual ammonia not recovered from the gases in primary scrubber 6.

The term lean is applied herein to absorbing media .in the sense generally used in the art, to indicate that a medium is deicient in the material which it is used to absorb. Thus a lean monoammonium phosphate solution as the term is used herein, is one which contains little, if any, ammonia, other than that chemically combined as (NH4)H2PO4, and therefore has the capacity to take up relatively large quantities of ammonia. Corr versely, a rich absorbing solution is one which contains large quantities of the material which it is used to absorb and, hence, can take up only a very small amount, or none at all of that material. As applied to the present application, a rich phosphate solution is one whose chemical composition approaches (NHQZHPOi. The mono-ammonium phosphate solution used in the scrubber 11 will have a ratio between about 1.1 and about 1.8, preferably between about 1.2 and about 1.4.

Moving out of ammonia scrubber lll, the gases are charged to a benzol scrubber 12, where they may again be contacted with an absorber oil, this time for the removal of light oils.

From the benzol scrubber 12, the gases may be delivered to fuel mains and burners for consumption.

Turning now to the circulating liquor in circulating liquor decanter 7, this is charged to a vacuum stripper rectifier 8. The vacuum stripper rectifier has an upper section 8a and a lower section 8b separated by an accumulator pan 8c having vapor risers 8d. In the upper portion of the vacuum stripper rectifier, the circulating liquor isiiashed under a pressure of between about 15 and about '5, say about 5 inches of mercury absolute to strip a major part of the acid gases and some of the ammonia from the circulating liquor. A part of the bottoms from this upper portion of the vacuum stripper rectifier is delivered to the lower portion of the rectifier. However, the major portion of the bottoms from the upper section of the vacuum stripper rectitier, after being cooled, is returned for use in the primary cooler.

In the lower section 8b of the vacuum stripper rectifier 8, the remainder of the bottoms from the upper section Sa is completely stripped. The resulting steam in admixture with ammonia moves through vapor risers 8d into the upper section 8a and aids in the stripping carried out in the upper section.

Advantageously, the heat content of the flushing liquor may be used for reboiling the liquor stripped in the vacuum stripper rectiiers bottom section although this is not shown in the ligure.

The ammonia and acid gases passing overhead from vacuum stripper rectilier 8, are condensed in condenser 13, the condensate being delivered to receiver 15. Vapors from receiver 15 are charged to vacuum absorber 14.

In the vacuum absorber 14, the gases are contacted with ammonia liquor to absorb the last traces of soluble gases. Fixed gases are removed from the system and discharged to the foul gas main as at 14a.

Condensate from the receiver l5, together with rich liquor from vacuum absorber 14, is charged to a rectifier ratio between about 1.4 and about 1.9, is steam stripped to produce ammonia vapor. The ammonia and steam from lower section 18 travel up through the vapor riser 16a and strip the condensate charged to upper section 17. The gases passing overhead from the upper section of rectifier concentrator 16 include ammonia, HCN, and H28. They are delivered to a gas absorber 19. The lean monoammonium phosphate bottoms stream having a ratio about 1.3, from the lower portion of rectifier concentrator 16 is recycled to ammonia scrubber 11, a part being drawn oi and sent to gas absorber 19.

In the gas absorber 19, the lean monoammonium pho-sphate selectivelyabsorbs ammonia and HCN. H25 passes overhead and is delivered to sulphur recovery plant 20 for further processing, not included within the scope of the invention.

The rich solution from gas absorber 19 having a ratio between about 1.6 and about 1.9, preferably about 1.7 is charged to a hydrogen cyanide stripper 21. From stripper 21, a gaseous hydrogen cyanide stream is taken oi overhead leaving a bottoms stream` of rich ammonium phosphate solution. A small amount of lean monoammonium phosphate solution to which has been added between about 0.5% and about phosphoric acid, is charged to the top of HCN stripper as at 22 in order to prevent ammonia from passing overhead with the hydrogen cyanide. The'HCN passing overhead from stripper 21 may be processed for further recovery (not shown).

The rich ammoniacal liquor from the bottom of stripper 21 containing between about 20 and about 50, preferably between about 35 and about 45 wt. percent total phosphate and having a ratio between about 1.6 and about 1.9, is charged to a lower section 25 of an ammonia stripper 23. There a portion of the ammonia content of the rich solution is stripped, preferably at a relatively high temperature, between about 140 C. and about 90 C., say about 130 C. and under a total pressure of between about atmospheric and about 75 p. s. i. g., say about 30 p. s. i. g. Such conditions are helpful in washing out pyridine. Y v

Vapor rising from the lower section 25 of ammonia stripper 23 passes through a chimney riser 27 to upper section 24 of the ammonia stripper 23. At this point, the ammonia-water mixture is contaminated only with pyridine and similar compounds. Advantage is taken of the relatively low volatilty of pyridine with respect to ammonia over aqueous solutions at low temperatures, and the relatively high volatility at high temperatures. Thus, with the tower 23 operating under the conditions described, pyridine is relatively easily washed from the ammonia in the upper section of the tower and stripped upwards from the ammoniacal solution passing down toward the bottom section. Thus, pyridine concentrates in an intermediate position in the tower. A pyridine-ammoniawater vapor mixture is withdrawn at this point, designated as 24a in Figure 1. It must be emphasized that in the stream 24a will be found substantially all the pyridine bases removed from the coke oven gases. In accordance with rthe invention, this stream at a temperature between about 50" C. and about 130 C. inclusive, preferably between about C. and about 100 C., is charged to tar bases springing tower 28. Its function there will be more fully described below.

The ammonia-water stream passing overhead from stripper 23 may be dehydrated as in caustic dehydrator 40 to produce anhydrous ammonia. A lean monoammonium phosphate solution having a HaPO4 Y ratio about 1.3, is drawn from the bottom of the lower section 25 of stripper 23 and used for scrubbing in ammonia scrubber 11. An ammonia-water solution drawn from the bottom of the upper section 24 of stripper 23 may be used for scrubbing in primary cooler 6.

Turning now to the tar which forms a lower layer in decanters 5 and 7, this is withdrawn and charged to a tar distillation system indicated generally as 29.

Details of the tar distillation system are not a part of this invention, and any of a number of different designs may be employed. Preferably, however, the tar distillation system is similar to thatdescribed and claimed in my copending application Serial No. 354,542, led May l2, 1953.4

Alternatively, the tar distillation systems described and claimed in the United States patents of Gerald L. Eaton, Numbers 2,649,403 and 2,639,405, and in the United- States patent to Thomas G. Reynolds No. 2,649,404 may be used.

As shown in the drawing, the tar drawn from the decanters 5 and 7 is charged to a tar dehydrating plant 30, where, by centrifugal action or other means, water is removed from the tar. The substantially dry tar is then charged to a tar fractionator 31, where an overhead stream comprising tar acids, tar bases, and a certain amount of neutral oils, such as benzene and naphthalene, is removed. A stream of higher-boiling materials may also be removed from fractionator 31, as at 31a, and processed in further distillation equipment (not shown).

The overhead stream from fractionator 31 is condensed as at 32 and the condensate is mixed with a dilute alkali, such, for example, as a solution containing between about 5% and about 50%, usually about 10% NaOH, for the extraction of tar acids.

n The mixture of alkali and tar constituents is charged to tar acid separator tank 33 where the alkali reacts with the tar acids to form the corresponding salts, such for example, as sodium carbolate. The tar acids form in a lower aqueous layer, which is drawn ott as at 34, leaving an upper layer which comprises neutral oils and tar bases. This upper layer is drawn olf through line 35. A mineral acid, such for example, as an aqueous solution containing between about 5% and about 50% by weight H2SO4, is mixed with the tar-base neutral-oil mixture in line 35 and this mixture is then delivered to tar bases separating tank 36. In the tank 36, the mineral acid reacts with the tar bases to form the corresponding salts of the tar bases, such as pyridine sulphate. These tar base salts form in a lower aqueous layer leaving an upper layer of neutral oil's which may be drawn off as through line 37 and charged to the tar distillation system for further recovery l(not shown).

The aqueous lower layer from tank 36 containing the *tar base salts of they mineral acid used, and a certain amount of neutral oils, are charged to oil stripper 38, where, by means of steam entering through line 39, the remaining neutral oils are removed overhead for further recovery.

The bottoms stream from oil stripper 38 comprising the acid-tar bases, in accordance with the invention, are then charged to tar bases springing tower 28. Here the acid-tar bases are contacted with hot vapor stream 24a drawn from ammonia fractionator 23, which, as pointed out above, contains substantially all the pyridine bases removed from the coke oven gases with theamrnonia.

In accordance with the invention, these hot ammonia pyridine-base vapors spring and strip the tar bases from the acid-tar bases stream charged to tower 23 from the bottom of oil stripper 38. .In performing this function, the ammonia drawn from ammonia stripper 23 acts to neutralize the acid in the acid-tar bases mixture, thus springing the tar bases, i. e., decomposing the tar base salts, leaving the tar bases free. The sprung tar bases are simultaneously stripped from the mixture and pass overhead along with water and the pyridine bases.

Thus, vthe invention conveniently permits both the pyridine Vbases and the tar bases to be recovered in a single stream.

A somewhat different embodiment of the invention is shown in Fig. 2.

Referring to Fig. 2, hot coke oven gases coming from coke oven l are charged to a collecting main 52 where they are contacted with anammoniacal scrubbing liquid as at 5S. By this means, the gases are cooled, a certain amount of ammonia is absorbed, and tar is precipi tated. The foul flushing liquor passes through downcomer 54 into flushing liquor decanter 55. The hot gases from downcomer '54 are carried to a primary cooler 56 where they are contacted with an ammoniacal circula*- ing liquor and are thereby further cooled. The used circulating liquor is discharged to circulating liquor decanter 57.

In the decanters 55 and 57, the flushing and circulating liquors separate into two layers, namely, a lower tar layer, and an upper aqueous layer. The upper aqueous layer from the flushing liquor decanter is drawn off and used again in the collecting mains. The water layer from the circulating liquor decanter is drawn off and used again in the primary scrubber.

The cooled gases passing out of the primary cooler are delivered to a naphthalene scrubber 5S where they are contacted with an absorber oil to remove naphthalene therefrom. In passing out of naphthalene scrubber 58, the gases move through a tar separation device such for example, as an electrostatic precipitator 59 where particles of entrained tar are removed.

The gases moving out of the precipitator 59 are delivered to a booster 60 where their pressure is raised to a degree dependent on the demand requirements and the pressure drop of downstream apparatus, but preferably to above about l2 pounds per square inch gauge.

The compressed gases are then delivered to an acid gas scrubber 6l where they are contacted with an ammoniacal scrubbing liquor which removes about 90% of the H28 and HCN and some of the CO2 along with about 80% of the ammonia.

From the acid gas scrubber 61, the gases are delivered to an ammonia scrubber 62 where they are contacted with cooled water delivered through cooling tower 63. for the removal of the remainder of the ammonia and the pyridine bases.

From the ammonia scrubber, the gases are charged to a benzol scrubber 64 where they are contacted with additional absorber oil to remove light oils. The gases now largely denuded of valuable oils may be delivered to fuel mains for burning.

The bottoms liquor from acid-gas scrubber 61 is split and a part is returned to the flushing liquor decanter 55. By this means the concentration of acid gases in the ushing liquor is increased. The flushing liquor is used to scrub the hot gases in the gas mains as pointed out above, and in the course of such scrubbing, volatile components of the ilushing liquor are vaporized. Hence the concentration of acid gases in the gas feed to the acid scrubber is increased. This, in turn, increases the concentration of acid gases in the bottoms removed from the acid gas scrubber, which reduces the volume of liquor, and the stripping duty required of subsequent apparatus.

That part of the bottoms stream from acid-gas scrubber 6l which is not returned to the flushing liquor decanter, is charged to a vacuum stripper-rectifier 65. The vacuum stripper-rectiiier 65 operates in substantially the same manner as the vacuum stripper-rectifier described conne `'l i. It has an upper and a lower section.

in 1e upper section, the liquor from the acid gas scrubber is partiallv stripped under approximately 5 inches of mercurypressure, to remove a major portion of. the gases and a small amount of the ammonia J' i the liquor.

lower uart of the vacuum stripper rectifier, a or the liquor which was partially stripped in the upper se: on is further stripped to remove ammonia. Heat for this stripping may be furnished by steam generated with the hot ilushing liquor. The bottoms water from the lower section of vacuum stripper rectifier 65 is cooled in cooler 63 and used for removal of residual ammo-nia in the ammonia scrubber 62.

The maior portion of the bottoms stream from the upper section of vacuum stripper rectifier 65 containing ammonia, is used to malte up the scrubbing liquor for acid scrubber 6i.

The overhead from vacuum stripper rectifier 65 contains ammonia and acid gases. lt is condensed in condenser 66. The uncondensed vapors from the condensation process are delivered to a vacuum absorber 67 where they are contacted with additional cold water to remove any soluble gases not removed in the condenser 66. The vacuum absorber 67 is preferably operated at a pressure ranging between about 3 inches and about 5 inches, say at about 4 inches of mercury.

The condensate from condenser 66 and the bottoms stream from vacuum absorber 67 are charged to a dissociator apparatus indicated generally as 70 which functions to remove from to 95% of the acid gases from the ammonia and pyridine bases.

The dissociator apparatus comprises a vacuum dissociator 68 and a pressure dissociator 7l. As shown in Fig. 2, these two units may be mounted vertically with the vacuum dissociator on top of the pressure dissociator.

The liquors from condenser 66 and absorber 67 are charged first to the vacuum dissociator 68 which operates at a pressure between about 3 inches and about 10 inches say at about 8 inches of mercury.

In the vacuum dissociator, the liquid feed is met by a hot gaseous stream of ammonia, acid gases and steam rising from the pressure dissociator 7i. A quantity of the acid gases and ammonia are vaporized and pass upwardly through the vacuum dissociator. As they move upwardly they are met by cool (say between 10 C. and about 25 C.) water from cooler 63 by means of which the ammonia is absorbed leaving the acid gases to pass off overhead.

The bottom stream from vacuum dissociator 68 is heated in heat exchanger 69 and charged to the pressure dissociator 71 which operates at a pressure between about 50 p. s. i. g. and about 200 p. s. i. g., say at about p. s. i. g. There it is stripped with steam introduced through line 'Ilia which removed from 90 to 95 of the acid gases and a considerable quantity of ammona.

These vapors, together with uncondensed steam are delivered to the vacuum dissociator 68 through line 71a, for the purposes described above.

The overhead from vacuum dissociator 63 consisting chieily of acid gases with a small amount of ammonia, is compressed to atmospheric pressure in compressor 84 and delivered to an ammonium sulphate scrubber 72. In the ammonium sulphate scrubber 72, the small quantity ,"9 of residual ammonia present in the compressed acid gases is scrubbed from them with dilute sulphuric acid containing for example, between about 0.5% and about 10% H2SO4 introduced through line 72a to produce ammonium sulphate.

The acid gases, now free of ammonia, are charged to an HCN absorber 73 where they are contacted with a solution introduced through line 73a. This solution is buffered to a pH between about 1 and about 6. By this means, HCN is substantially completely absorbed allowing HzS to pass overhead through line 73h and eventually to be delivered to a sulphur recovery plant (not shown).

The bottoms stream from hydrogen cyanide absorber 73 is delivered through line 73C to an HCN stripper 74 where' it is stripped with steam introduced through line 74a. HC is removed overhead through line 74b and may be recovered in further processing equipment (not shown).

The bottom stream from pressure dissociator 61 is delivered through line 711Mo an ammonia' stripperjs where it is substantially completely stripped of its soluble gas content using live exhaust steam. w

The overhead from the ammonia stripper 75 contains water, ammonia, and the pyridine bases which were removed from the coke oven gases in the acid gas scrubbers and in the ammonia scrubbers. This overhead stream is delivered to a pure ammonia tower 76 where it is scrubbed with cold (between about 10 C. and about C.) water, introduced through line 76a, to remove pyridine and other organic compounds.- A first portion of the bottoms stream from the pure ammonia tower is recycled to the top tray of the ammonia stripper as through line 76h. Substances whose volatility lies between that of ammonia and water thus tend to concentrate in the liquid and vapor passing back and forth between these two towers.

A second portion of the liquid bottoms from tower 76 are delivered to the acid gas scrubber 61 through line 76C.

In accordance with the invention, a third portion of this liquid is used to spring the tar bases, previously removed from the tar, as will be described below.

Returning now to the tar layers in the bottom, of the flushing and circulating liquor decanters 55 and 57, respectively, this tar is delivered to a tar purification plant 78 where the major portion of the water content of the tar is removed, either by flash distillation or pressure separation, both of which are described, for example, in the copending application of Thomas G. Reynolds, Serial No. 186,887, led September 26, 1950, or by centrifugal means. The purified tar is then heated as in heater 79 and delivered to a tar fractionating system 80, preferably in admixture with the naphthalene-rich absorber oil drawn from naphthalene scrubber 58 through line 58a as described, for example, in Patent No. 2,649,403 of G. L. Eaton. The particular tar fractionating system employed is not a part of this invention and may be that described in the Eaton patent referred to, or the patent to Thomas G. Reynolds, No. 2,649,404, referred to above. Preferably, however, the `distillation system described in my copending application, Serial No. 354,542, led May l2, 1953, is employed.

The overhead from the distillation system 80 contains light oils, tar bases, and tar acids. It is condensed as at 81 and mixed with a basic liquid, such for example as an aqueous solution containing between about 5% and about 50% by weight sodium hydroxide, introduced through line 82a.

The mixture is then charged to a tar acid separation tank 82. Here the caustic reacts with the tar acids to form for example, sodium carbolate which collects in an aqueous lower layer, leaving the tar bases and neutral oils in an upper phase. The upper phase is drawn olf, through line 82h, mixed with dilute sulphuric acid containing, for example, between about 5% and about 50% H2804, entering through line 83a and charged to tar bases separation tank 83.

In' tar' bases separation tank 83, the sulphuric acid reacts with the tar bases to form tar base sulphates, which collect in a lower aqueous layer, leaving an upper layer of neutral oil.

l The lower aqueous layer is removed through line 83b andcharged to an oil stripper 85. The neutral oils may be withdrawn through line 83C and sent to further distillation equipment (not shown).

ln oil stripper 85, the aqueous material containing the tar bases is stripped of whatever neutral oils are still present by means of steam introduced through line 87. Thelneutr'al oils may be subjected to further distillation.

The bottoms from the oil stripper 85 drawn off through line 89 contains the tar bases present as their salts for example, as sulphate's.

In accordance with the invention, this bottoms stream is mixed with a portion of the bottoms from the pure ammonia tower 76 owing through line 91 and the mixture is charged to a springing drum 93, through line 92. In' the drum 93, the ammonia reacts with the tar base sulphates, forming ammonium sulphate and releasing 'the tar bases, which with the pyridine bases entering through line 91 form a pyridine-tar bases layer in the upper part lof drum 93, whence it can be withdrawn as product through line 94. The ammonium sulphate solution forms a lower layer in drum 93, whence it can ybe-vvithdrawn through line 95 and treated for recovery of the salt, if desired.

It must be emphasized that the process described above and the'gures given in connection therewith, are introduced for purposes of illustration only. As pointed out above, other variations of the basic Cole-Tannehill processlmay be employed, or processes not related to the basic Cole-Tannehill method may be us'ed. Where in the specific description sodium hydroxide is used, it is obvious that other alkalis, such as potassium hydroxide, may also be used. Where sulphuric acid is employed, generally speaking, other mineral acids, such as phosphoric or hydrochloric, may be substituted.

In the process of Fig. l, the ammonia-pyridine base stream used in springing the tar bases is a gaseous stream, While in Fig. 2 a liquid stream is employed. It will be understood that if desired, a liquid stream may be used for this purpose with the process of Fig. l, and a gaseous stream with the process of Fig. 2.

Finally, although separation of tar acids from a mixture of tar acids, tar bases, and neutral oils is shown using a mineral alakli, such as caustic soda, it will be evident that any relatively polar compound which will react selectively with the tar acids, such for example as ethylene glycol, may be used, followed by a liquid-liquid extraction.

Alternatively, and depending on the composition of the tar, other means of isolating the tar bases, such as fractional distillation or fractional condensation, may be employed.

What I claim is:

l. In a coke oven by-product recovery process, a method for recovering tar and pyridine bases which comprises removing tar and tar bases from hot coke oven gases, subsequently scrubbing said gases to remove ammonia, acid gases and pyridine bases therefrom with the production of an aqueous liquor containing ammonia, acidgases and pyridine bases, isolating said tar bases in an aqueous acid-tar bases liquor, treating said aqueous liquor containing ammonia, acid gases and pyridine bases to produce a stream containing ammonia and pyridine bases which is substantially free from acid gases, concentrating the pyridine bases in said stream, and contacting said acid-tar bases liquor with at least a portion of the concentrated ammonia-pyridine base stream, thereby springing said tar bases from said acid-tar bases liquor, removing ammonia from said concentrated stream, and

combining the pyridine and tar bases in a single stream.

2. The method claimed in claim 1, wherein the aqueous liquor containing ammonia, acid gases and pyridine bases is treated to produce a gaseous stream containing ammonia and pyridine bases, substantially free from acid gases.

3. The method claimed in claim 1, wherein the aqueous liquor containing ammonia, acid gases and pyridine bases is treated to produce a liquid stream containing ammonia and pyridine bases, substantially free from acid gases.

4. The method claimed in claim 1 wherein the ammonia, acid gases and pyridine bases are removed from said gases by scrubbing with a monoammonium phosphate solution.

5. in a coke oven by-product recovery process a method for recovering tar and pyridine bases from hot coke oven gases which comprises scrubbing said gases with an aqueous liquor to remove tar and tar bases therefrom, extracting the tar bases from a mixture of tar bases and other tar components by means of a mineral acid to form an acid-tar bases liquor, scrubbing said gases subsequent to the removal of tar and tar bases therefrom with an aqueous mono-ammonium phosphate liquor to remove ammonia, acid gases and pyridine bases therefrom, with the production of an aqueous liquor containinc7 ammonia, pyridine bases and acid gases, treating the last-named liquor to produce a gaseous stream containing ammonia and pyridine bases substantially free from acid gases, concentrating the pyridine bases in said stream, and contacting said acid-tar bases liquor with at least a portion of the concentrated ammonia-pyridine base stream, thereby springing said tar bases from said acidtar bases liquor, removing ammonia from said ammonia pyridine base stream, and combining said tar and pyridine bases in a single stream.

Vfrom and to produce a liquor containing ammonia, acid gases and pyridine bases, then further scrubbing the coke yoven gases with water to remove substantially the remainder of said ammonia and pyridine bases and to give a liquor containing ammonia and pyridine bases, treating the two East-named liquors to remove ammonia and pyridine bases therefrom and to separate said ammonia and pyridine bases from acid gases, absorbing the ammona and pyridine bases so separated in an aqueous liquor and commingling the last-named liquor with said acid-tar bases liquor to spring said tar bases from said acid-tar bases liquor, whereby the tar bases and the pyridine bases may be recovered in a single stream.

References Cited in the le of this patent UNITED STATES PATENTS 1,274,998 Dodge et. al Aug. 6, 1918 2,162,838 Cole et. al. .lune 20, 1939 2,284,460 Wells et. al May 26, 1942 2,388,475 Engel Nov. 6, 1945 2,518,353 McKinnis Aug. 8, 1950 2,649,403 Eaton Aug. 18, 1953 2,649,404 Eaton Aug. 18, 1953 2,720,526 Sweeney Oct. 11, 1955 

1. IN A COKE OVEN BY-PRODUCT RECOVERY PROCESS, A METHOD FOR RECOVERING TAR AND PYRIDINE BASES WHICH COMPRISES REMOVING TAR AND TAR BASES FROM HOT COKE OVEN GASES, SUBSEQUENTLY SCRUBBING SAID GASES TO REMOVE AMMONIA, ACID GASES AND PYRIDINE BASES THEREFROM WITH THE PRODUCTION OF AN AQUEOUS LIQUOR CONTAINING AMMONIA, ACID GASES AND PYRIDINE BASES, ISOLATING SAID TAR BASES IN AN AQUEOUS ACID-TAR BASES LIQUOR, TREATING SAID AQUEOUS LIQUOR CONTAINING AMMOMIA, ACID GASES AND PYRIDINE BASES TO PRODUCE A STREAMM CONTAINING AMMONIA AND PYRIDINE BASES WHICH IS SUBSTANTIALLY FREE FROM ACID GASES, CONCENTRATING THE PYRIDENE BASES IN SAID STREAM, AND CON-TACTING SAID ACID-TAR BASES LIQUOR WITH AT LEAST A PORTION OF THE CONCENTRATED AMMONIA-PYRIDINE BASE STREAM, THEREBY SPRINING SAID TAR BASES FROM SAID ACID-TAR BASES LIQUOR, REMOVING AMMONIA FROM SAID CONCENTRATED STREAM, AND COMBINING THE PRYIDINE AND TAR BASES IN A SINGLE STREAM. 